10
The last series of experiments, to which we refer in this
paper, were done on the latter model; for the purposes of the
photographs it was placed in a vertical position and was joined
to the support trestle with special rods,
A whole series of auto-adhesive pegs were put on the mo-
del, both on the metal part and on the panel; these marks, con
sisting of a black cross, 1 cm in diameter and 0.1 mm thick,
were put on following pre-arranged lines, and their distribu-
tion can be seen in Fig. 3.
On the metal part we put 20 pegs; on the panel 30 pegs.
Given that the photographs were all taken at the same di
stance from the object, and given that the principal distance
of the 3 cameras used was different, the photographic dimension
of the lines of the pegs came out slightly too thin with the
TMK Zeiss camera, and slightly too thick with the Contonar - 6a
lileo. With the P31 Wild camera, however, they were excellent.
The whole model was accurately surveyed, for the purposes
of determining the spatial co-ordinates of all the points mar-
ked, in relation to en origin fixed at point 99, (see Fig, 1),
using the Beta 3D/DEA measuring and tracing equipment.
This machine consists of a table and a head which can be
moved according to the three orthogonal directions, with the
following strokes: X = 1000, mm Y = 1800 mm, Z = 700 mm. The
mobile head can support either a collimator or a stylus.
With the object fixed on the table, we first used the
collimator to determine the X, Y co-ordinates of the marks, bo
th on the panel support and on the sheet metal piece.
These co-ordinates were recorded, using a tape-recorder
and data puncher. Then, going back automatically to the collima
ted points, the reading of the third co-ordinates was done,
with the help of the stylus. This procedure eliminates the pro
blem of evaluating the positioning of the stylus on the marks
to be examined, a difficult and subjective evaluation even usi
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